I had a LOT of books read to me, and I read a lot of books about Alzheimer's disease.
I have never found such a perfect explanation of Alzheimer's disease and how it effects the brain than this one, by Dr. Max Wallack. He compares the loss of brain signals to not catching a baseball. (Dr. Max also drew the pictures!) It is from his amazing book, Why Did Grandma Put Her Underwear In The Refrigerator? An Explanation of Alzheimer's Disease for Children. The illustrations are wonderful. The storyline is realistic and it helps kids (and their parents) with difficult questions. It was based on experiences with my grandma and his great grams Gertrude.
To order it click here